Recent work indicates that vomeronasal and taste transduction in vertebrates share similar transduction pathways: G protein-coupled receptors signal through phospholipase C (PLC) to open a member of the TRP family of ion channels, TRPC2 for the vomeronasal organ (VNO) and TRPM5 for taste. The importance of these ion channels for chemosensation is highlighted by the lack of response to pheromones in TRPC2 knockout mice and to bitter, sweet and amino acid tastes in TRPM5 knockout animals. Understanding the mechanisms by which TRP ion channels are gated, has proven difficult in any system, and remains an essential goal for understanding taste and VNO transduction. In the last grant period, we discovered that TRPM5 is activated by intracellular Ca +, suggesting that Ca + may be the second messenger for some forms of taste transduction. In the next grant period we aim to understand the molecular mechanisms that underlie regulation of TRPM5, and how molecular properties of TRPM5 influence taste sensation. We will specifically address the following questions: (1) What are the mechanisms by which TRPM5 channels are activation and inactivated? In these studies we will use patch-clamp recording of expressed TRPM5, together with pharmacological and structural manipulations of the channel. (2) Do blockers of TRPM5 interfere with taste detection? Blockers will be identified by patch-clamp recording from cells expressing TRPM5 and the effects of identified blockers on taste thresholds in mice will be determined (3) Do similar channels to TRPM5 play a role in VNO transduction? TRPM5 and related channels are widely expresed in the body, and mutations in these channels may underlie certain pathological states. By understanding the regulation of these channels, we can understand their contribution to signaling in health and disease.